Re: foreign predicate not working

[Paulo Moura]

On 19/jul/2004, at 15:25, Saurabh Bhatla wrote:

> Hi
>   I am using a foreign predicate from my logtalk object. I define that
> in a file receiver.lgt (attached). the definition of my predicate is in
> file file_ops.c (attached). I can compile the code in gprolog and am
> able to make an executable out of it too. The problem is that whenever 
> i
> call the foreign predicate it returns false. I have some printf
> statements in my C code but none of them gets printed, which mean that
> the c code is not being called at all.
>   I tried to trace the execution and the call to my foreign predicate
> simply fails without checking anything. My C program works fine when
> executed alone.

Your definition of the Logtalk object receiver seams to be wrong. The 
code you sent us is:

:- foreign(get_event_ob(+string,-string)).

:-object(receiver).

        :-public(receive/1).
        :-public(validate/1).
        :-public(get_event_ob/2).
        
        receive(Event).

        validate(Event):-
                self(Self),
                Self::get_event_ob(Event,Object),
                write(Object),  
                write('<-object found for event->'),
                write(Event),nl.

        validate(Event):-
                write('No object found for event->'),
                write(Event),nl.
                
:-end_object.

The problem is that the predicate get_event_ob/2 is not defined inside 
the object "receiver". You need to write:

        validate(Event):-
                self(Self),
		{get_event_ob(Event,Object)},	% external call; the {}/1 construct 
bypasses the Logtalk pre-processor
                write(Object),  
                write('<-object found for event->'),
                write(Event),nl.

Cheers,

Paulo


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Paulo Jorge Lopes de Moura
Dep. of Informatics                   Office 4.3  Ext. 3257
University of Beira Interior          Phone: +351 275319700
6201-001 Covilhã                      Fax:   +351 275319891
Portugal

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<http://www.di.ubi.pt/~pmoura>     <http://www.logtalk.org>
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